1. Field of the Invention
The present invention relates to a semiconductor laser source for use in a laser beam printer, a laser facsimile apparatus, an image scanner for printing, a bar code reader, a copying apparatus, and a sensor.
2. Description of the Prior Art
A semiconductor laser source is used for various apparatuses such as the above-mentioned ones as an optical system using the coherence of a laser beam (e.g. as an optical pickup which is an application of a characteristic of the laser beam that it can be converged into a minute spot). In such an optical system, the light source has been reduced in size to reduce the power consumption. The size of the optical system has also been reduced. For example, as a lens system for coupling laser beams, the minute one with a diameter of several millimeters is known.
In the above-mentioned optical system, as shown in FIG. 1, a laser beam LB emitted from a semiconductor laser 1 is divided into a component A directly passing through a first surface S.sub.1 and a second surface S.sub.2 of a lens 2 and a component B first reflected by the second surface S.sub.2 and first surface S.sub.1 and then passing therethrough. Thus, the optical path lengths of the components A and B are different. Since the laser beam is highly coherent, deformation of a beam intensity pattern due to interference between the components A and B, that is, non-uniformity of a beam intensity (interference fringe) is caused in a beam spot formed. This nonuniformity of the beam intensity brings about various problems. For example, in a case where the optical system is employed for a sensor, noise increases when only a part of a laser beam is received by a sensing device, which may result in a malfunction.
In order to prevent the generation of nonuniformity of the beam intensity, generally, the lens is anti-reflection coated. The reflection prevention processing is performed by setting a plurality of lenses one by one at a planetary in a vacuum chamber and then applying to them a multi-layer coating including magnesium fluoride and titanium dioxide.
However, since a portion of the lens used to hold the lens is reduced because of the reduced size of the lens, setting of the lens in the above-mentioned multi-layer coating process is difficult, which complicates the work. In addition, the multicoating results in an increase of the cost.